The general goal of this project is to (i) examine the peripheral central nervous system mechanisms and interactions which produce changes in aggressive state (using the American lobster, as the crustacean model system); and (ii) to determine the physiological and morphological basis of single neurosecretory neurons affecting aggressive behavior. Serotonin neurons, responsible for modulating aggression in lobsters have been identified at a morphological and physiological level. Specifically, I will focus on a sub-set of neurosecretory neurons, namely the spontaneous serotonin neurosecretory cells (A1-5HT). The properties of the ionic currents which determine spontaneity of these cells will be identified and quantified. Furthermore, the physiological affect of perfused serotonin and 20-hydroxyecdysone, the crustacean molting hormone, on the ionic channel properties of Al ganglion-secretory containing neurosecretory neurons, will be further explored. Both standard electrophysiology combined with voltage clamping (the major technique to be learnt in this NRSA grant period), will be used to describe the relationship of ionic currents with each other and their interactions relating to behavioral modulation at both the central and peripheral nervous systems. In summary, the ionic channel properties of these neurosecretory cells will be examined and identified.